Preterm Births Predicted by Cervical Microbiota and Immunity

Spontaneous preterm birth (sPTB), defined as birth before 37 weeks of gestation, is the largest contributor to infant death worldwide, according to the World Health Organization. Babies that survive preterm birth often face costly lifelong health problems, including respiratory difficulties, vision loss, cerebral palsy, and intellectual delays. In a study published today in Nature Communications, researchers discovered that bacteria and innate immune factors in a woman’s birth canal and cervix may increase the risk of spontaneous preterm birth or provide protection against such births.

In this study, researchers examined vaginal swabs from a sample of 2,000 pregnant women taken at three distinct points in pregnancy to determine the bacteria that made up the cervicovaginal microbiota. Using innovative modeling of the cervicovaginal microbiota, seven bacteria were significantly associated with increased risk of spontaneous preterm birth, with a stronger effect seen in African–American women. Interestingly, higher vaginal levels of the antimicrobial peptide β-defensin-2, a part of our innate immune system, lowered the risk of sPTB associated with cervicovaginal microbiota in an ethnicity-dependent manner.

“Predicting prematurity has been a riddle that has troubled researchers and clinicians for years, but we are finally shedding light on a path toward offering treatment to women we can identify as being at risk,” says co–senior author Jacques Ravel of the University of Maryland. “Previous studies, including ours, were limited by low sample size. In establishing this large cohort, we aim to identify factors early in pregnancy that could be used to predict the risk to spontaneous preterm birth.”

These findings hold promise for diagnostics to accurately identify women at risk for sPTB early in pregnancy. Therapeutic strategies could include immune modulators and microbiome-based therapeutics to reduce this significant health burden.

“Approaching this complex health problem of preterm births from a multidisciplinary perspective is given clinicians new insights,” says University of Maryland Dean E. Albert Reese, who was not an author of the study. “While there is known racial disparity in preterm births with African–American women having significantly higher rates than non-African–American women, factors that underpin this disparity have remained elusive.”